Pinpointing Planets in Circumstellar Disks

Abstract

A crowning achievement in mathematical science was the prediction by Urbain Le Verrier and John Couch Adams in 1845 of a previously unknown planet that was then subsequently discovered. Irregularities in Uranus's orbit were elegantly explained as being due to a single massive object exerting perturbations on Uranus and the position of the object in the sky was predicted. The planet Neptune was subsequently detected by Johann Gottfried Galle at the Berlin Observatory (cf.[1]). Planets can not only perturb each other, as outlined in the original perturbative theory by Laplace, but also perturb the orbits of smaller particles such as dust that can be much more numerous and so can reemit a detectable fraction of the host star luminosity. Disk morphology can provide dynamical evidence for massive bodies that can be subsequently discovered from direct observations. We can refer to historical examples in our solar system. For example, the prediction of a satellite in the Encke gap in Saturn's rings based on wavy edges seen in the gap [2], was followed by the discovery of the satellite, Pan [3].In this chapter, a broad base of dynamical work relating circumstellar disk morphology to underlying planetary architecture is reviewed. The existence of a planet was predicted on the basis of its interactions with the circumstellar disk in the Fomalhaut system [4] at a semimajor axis of 119 AU. Subsequently, a planet was discovered with an estimated semimajor axis of 115 AU [5], only 4 AU lower than predicted. This is the first planet whose existence was successfully predicted from its interactions with the surrounding circumstellar disk (see Figure 2.1). discovery illustrates that we can, in some cases, predict the presence of planetary bodies from their interactions with disk material. The discrepancies between the predicted planetary orbit and mass from those inferred from observations are and will continue to be interesting. In probing them, we will improve our theoretical understanding and extend our capabilities so that we can accurately infer planetary system architecture at levels below the concurrent detection limits. In this chapter, we discuss some of the broad foundation of work that this prediction and others are built Formation and Evolution of Exoplanets. Edited by Rory Barnes